Mobile communication systems refer, in general, to different telecommunication systems providing personal wireless data transmission while subscribers roam the system area. A typical mobile communication system is the public land mobile network PLMN.
Besides conventional speech transmission, digital mobile communication systems provide a plurality of services: short messages, facsimiles, data transmission, etc. Of these, the data transmission service, in particular, provides a mobile subscriber a chance of wireless access to nearly all data services of fixed networks.
The use of the TCP/IP (Transmission Control Protocol/Internet Protocol) data network, i.e. the Internet network, in fixed networks has increased very rapidly. As is well known, the Internet network actually comprises a large number of smaller interconnected TCP/IP networks. The Internet network has a number of TCP/IP application protocols available for users. From the end user's point of view the most important ones are the following:                TELNET. This protocol allows the user's terminal (or user application program) in one computer to communicate with an application process, e.g. a word processing program run in a remote computer, in another computer via the Internet network as if the user's terminal were directly connected to the other computer;        FTP (File Transfer Protocol). This protocol allows the user's terminal (or user application program) to access a remote file system and to interact with it;        SMTP. This protocol provides a network-wide mail transfer service between e-mail systems of different computers;        WWW (World Wide Web). The WWW system consists of servers in the Internet network and customer programs used by these servers, called WWW browsers. The information in the WWW servers is arranged into pages which are the basic units of the WWW techniques, as whole pages are always transferred between a server and a browser. In addition to text, the page may also contain graphics and various other file types, such as voice and video. The pages used by the WWW techniques are described with the HTML language (Hyper Text Mark-up Language). Information on text format, graphics, etc. is coded among the actual text contents by HTML tags. The browser program uses these tags to give a WWW page the desired format.        
Internet applications are used for connecting to services in the Internet network. Before a user can connect to the Internet, he has to have a contract with an Internet service provider ISP, who provides access to the Internet via one or more Internet access points IAP. The ISP may be e.g. a commercial operator (as Eunet in Europe), university or private company. Usually, the IAP is a server to which the user has access from a telephone in the fixed network or from a mobile telephone by making a modem call (or a data call) to a certain IAP access number.
Through the data transmission services of mobile communication systems, the numerous information sources of the Internet network are, in principle, available to mobile subscribers, too. However, the user of data transmission services typically requires a mobile station provided with data transmission properties, and a computer connected thereto. At present, mobile stations including an integrated computer, such as the Nokia Communicator 9000, are available. This also has built-in facilities for connecting to the Internet network.
An ordinary subscriber of the fixed network usually need only one IAP, the one that is closest to him, and thus has the lowest call costs. A mobile subscriber may, however, roam within a large area in one country and even between different countries. If the mobile subscriber always uses the same IAP (home IAP) to connect to the Internet, call costs (data transmission costs) may increase considerably. For example, if the subscriber is roaming in Germany and his home IAP is in Finland, the use of Internet services via the home IAP entails an international call between Germany and Finland. To optimize data communication costs mobile subscribers would like to use the local IAP regardless of their location. The subscriber's Internet service provider ISP (as Eunet) may have numerous IAPs available all around the world. As regards a mobile subscriber, selecting the best possible IAP easily and, if possible, automatically may be problematic.
According to one method of the prior art, the subscriber manually reconfigures/changes/establishes a new IAP when he is in a new area. To carry out this subscriber needs a list of available IAPs telling how to set the correct IAP depending on the location of the subscriber. Manual configuration is, however, troublesome and error prone. Furthermore, the lists would not be up to date in the long run. For example, the Nokia Communicator 9000 is provided with a user interface supporting such as IAP list. The list may include e.g. the following information: 1) service provider's name; 2) telephone number of the IAP; 3) user's name (used in PPP authentication, if necessary); 4) password (used in PPP authentication, if necessary); 5) subscriber's own IP address; 6) IP addresses of the primary and secondary name servers.
In the case of the Nokia Communicator 9000 the service provider ISP is able to configure an IAP with a special short message, called SIAP SMS (Set Internet Access Point Short Message). This special short message carries out all necessary IAP settings in the mobile station and adds a new IAP to the list. The mobile station, however, asks the user to confirm the change before any action is taken. An advantage of this semi-automatic short message updating is that the user does not need to update information manually, which also eliminates errors. If this feature were used for supporting roaming, the user would need to call the service provider's customer service and to request information on the best IAP with respect to his location in a SIAP short message. From the user's point of view this is troublesome and may cause a considerable amount of extra work to the service provider, especially when the number of subscribers is large. Alternatively, the ISP could send a SIAP short message(s) to all subscribers when an IAP configuration has changed in some part of the world. This is, however, an inconvenient and expensive solution both for users and internet service providers.